1. Field of the Invention:
The present invention relates to electrical apparatus, and more particularly, to current limiting circuit interrupters having pivoting contact arms.
2. Description of the Prior Art:
Circuit interrupters are widely used to provide protection for electrical distribution systems against damage caused by overload current conditions. As the capacity of power sources increased, it was necessary to provide increased interrupting capability for circuit breakers to properly protect the electrical distribution system. In order to provide this protection in a more economical manner, current limiting circuit interrupters were developed to limit the flow of fault current to a level below that which the source was capable of supplying.
One type of current limiting circuit interrupter employs a high-speed mechanism to rapidly separate the contacts upon occurrence of a fault condition to draw an arc therebetween, allowing the voltage drop across the arc to limit the current flow. The electrodynamic force produced by the overload current flow through the circuit interrupter is used to rapidly separate the contacts and drive the arc into an extinguishing device. The standard trip mechanism then actuates to maintain the contacts in the open circuit position.
All types of circuit breakers require a certain amount of contact closing force to reduce resistance between the contacts and, consequently, the amount of resistance heating generated during normal closed circuit conditions. This contact force is most commonly obtained by means of extension or compression springs attached to the contact support arm. The higher the current rating of the circuit breaker, the greater the required contact force.
It is desirable to provide a current limiting circuit breaker having a pivoting contact arm which provides sufficient contact closing force yet assumes open and closed circuit positions which minimize contact wear. In addition, it is desirable to provide such a circuit breaker employing a magnetic drive slot motor to aid in rapidly separating the contacts during extreme overcurrent conditions.